1. Field of the Present Invention
The present invention relates generally to respirator apparatuses, and, in particular, to a portable powered air-purifying respirator utilizing one or more enclosed filters.
2. Background
A variety of apparatuses for providing breathable air in hazardous environments are well known. Two particularly common types are the air filtration type, in which ambient air is filtered to remove harmful contaminants so that the air may be breathed safely by the user, and the self-contained breathing apparatus (“SCBA”) type, in which a pressure vessel containing a supply of breathable air is carried by the user and used as necessary. Each of these types has been in use for decades.
More recently, these two types of apparatuses have been combined to provide greater flexibility for the user. A combination SCBA/air filtration respirator can be used by civil defense workers, first responders, HazMat teams and military forces to allow users the ability to increase their dwell time in an environment that is or could be contaminated with materials or chemicals harmful to the respiratory tract. The SCBA provides respiratory protection by providing the user a supply of air from a pressure vessel. The air filtration respirator employs filter canisters which filter the harmful materials or chemicals from the air provided to the user. The air filtration respirator can take one of two forms: either a purely negative pressure device or a blower assisted device. In a purely negative pressure air filtration respirator the user is required to draw air through the filter canisters with his lungs. In a blower assisted device, the user is assisted in drawing the air through the filter canister by means of an electronic blower inline with the air flow. The blower assisted device is typically referred to in the industry as a Powered Air Purifying Respirator (“PAPR”).
Current respirator configurations are typically limited to either a respirator used for air filtration or a respirator that provides a positive pressure supply of air from a pressure vessel. By providing both types of respiratory protection, a user is able to dwell in an area of potential contamination, or an area of contamination that is not classified as immediately dangerous to life and health (“IDLH”) by using the air filtration mode of respiratory protection. Then, if the user is required to enter an IDLH environment or the current environment becomes IDLH, the user is able to switch to SCBA respirator and to breathe supplied air from a pressure vessel. Finally, the user is able to switch back to the air filtration mode after exiting the IDLH environment, and maintain respiratory protection for exiting the environment and or throughout the process of decontamination. The important factor is to allow the user to switch back and forth between breathing modes without exposing the user to the ambient environment.
An example scenario for the use of such a configuration would be that of a HazMat team working to clean up a hazardous chemical spill inside of a large building. While at the site of the spill the users will require the respiratory protection of an SCBA. However, they must transit a large distance through the building to the actual site of the spill. During this transit the user also requires respiratory protection, although the respiratory hazard only requires an air filtration protection. If this scenario were played out with a user equipped only with an SCBA, one can readily see that the actual dwell time at the spill site is reduced, since a portion of the compressed air used by the SCBA is consumed in transit into and out of the building. If the user was equipped with a combined SCBA/air filtration respirator, the transit into and out of the building can be performed using the air filtration respirator, and the SCBA used only when needed at the spill site. In this way, the user will be able to maximize their time to accomplish their mission.
Another example scenario for the use of such a configuration would be that of a military fire fighter:                Personnel in a military fire-fighting unit are each equipped with the combination SCBA/PAPR respirator. The SCBA is used without the PAPR during normal fire fighting duties.        In the event of a chemical or biological attack, the fire fighting personnel will each don the facepiece and PAPR, wearing this configuration as long as the they are in a stand-by condition, and as such are protected from the chemical or biological environment.        If, during the chemical or biological attack, and while wearing the PAPR, the personnel are called on for fire fighting duties, the PAPR can be attached to the SCBA and the combined unit can then be donned. The user can then switch to the SCBA as necessary for fire fighting.        Upon exiting the fire environment, if a user has been contaminated by the chemical or biological attack, he will switch to the PAPR, then doff the SCBA and remove the PAPR from the SCBA. Throughout this cycle the user has maintained his respiratory protection, and is now ready to proceed a decontamination cycle.Combining the two types of respirators may not be a new concept; however the method of combining the two, as well as their configurations described below are unique and novel.        
Another issue with regard to conventional PAPR designs is that they merely provide a breathing assist to the user, and allow the facepiece pressure to go negative in cases of heavy respirations. Unfortunately, this often causes the user's face seal to leak, thus exposing the user to the ambient environment. This may be prevented by maintaining positive pressure inside the user's facepiece. However, in order for the PAPR to provide the user with enough air flow to maintain positive pressure, even at high respiratory rates, a constant high flow of air must be generated. Testing has shown that respiratory rates for heavy work can be on the order of 100 liters per minute (“lpm”). If a sinusoidal breathing cure is assumed for human breathing, this equates to peak air flow rates in excess of 300 lpm. This means that for the PAPR to maintain positive pressure, a flow rate of at least 300 lpm should be provided to the facepiece. The problem that this situation presents relates to the exhalation of the user. First, the user only actually needs a 300 lpm or higher flow rate for a small portion of each breathing cycle; the remainder of the air supplied to the facepiece is dumped out of the exhalation valve of the facepiece. This represents air that was filtered and not used by the user. Second, with this flow of 300 lpm or higher entering the facepiece, the same peak flows apply when the user is in the exhalation portion of the breathing cycle, which means that the exhalation valve must be capable of handling 600 lpm or higher peak flows (PAPR supplied flow+user exhalation flow). In order to accommodate flows of this magnitude without presenting high exhalation pressures to the user, overly large exhalation valves are required. Thus, a need exists for an improved approach to dealing with this problem.
Yet another issue with regard to conventional PAPR designs is that they are not intended to be carried into fires or other high-heat environments. The filter canisters used in typical PAPR's are not constructed to withstand flame, high heat or the like because such requirements have rarely heretofore been necessary. One recent approach to protecting the filter canisters is to cover each canister with a “bootee” to protect it until the canister is to be used. Unfortunately, such a design requires the additional step of removing the bootee, which is time-consuming and awkward. In addition, once removed, the bootees must be carried or stored safely, which is bothersome for the user. Still further, neither the bootees nor any other known device provides means for closing off air access to the filter canisters, for balancing the air flow between filter canisters when a plurality of filter canisters are utilized and thereby providing uniform wear on the filter canisters, or for otherwise providing functionality only available through the usage of an enclosure to control air flow in and out of the filter canisters.